This invention relates to a magnetic recording and reproducing device such as an R-DAT (rotary head type digital audio tape recorder) which performs recording and reproduction with a rotary head having plural heads of different azimuths and, more particularly, to a magnetic recording and reproducing device capable of reading information recorded in the form of a control such as a sub-code representing a musical piece, position or time or the like in a stable manner without dropping of such information over a long period of time during multiple speed or high speed reproduction in which reproduction is made by fast feeding or fast rewinding the tape.
The R-DAT is a device which converts analog signals such as an audio signal into PCM signals, records the PCM signals on a magnetic tape and reproduces the same.
As shown in FIG. 2, the device comprises a rotary head 2 having two magnetic heads A and B separated by 180 degree interval on the circumferential surface of a cylinder 1. A tape 3 is loaded from a cassette housing 4 with a vertical post 5 or with an inclined post 6, wound on the circumferential surface of the rotary head 2 for 90 degrees, supported by a fixed guide 7, and run by a capstan 8 and a pinch roller 9.
The diameter of the rotary head 2 is 30 mm, and the winding angle for the tape is 90 degrees. For recording and reproduction, at the mode I which is usually used, the speed of the rotary head 2 is 2,000 rpm (circumferential speed: 3.14 m/sec) and the speed of the tape 3 is 8.15 mm/sec in the direction identical to that of the rotary head 2. The relative speed of the head 2 as against the tape 3 is 3.13 m/sec.
The recording system with R-DAT is a helical scanning azimuth recording. Its tape format as shown in FIG. 3 defines the track angle as 6.degree. 22' 59.5" and azimuth angle as .+-. 20.degree. with the tracks alternately traced by two heads A and B.
FIG. 4 shows a track format wherein audio data are recorded at the center of a PCM region, and sub-codes and control signals such as ATF (automatic track finding) are recorded on both sides thereof.
The PCM region comprises 128 blocks as shown in FIG. 5 each of which has recording regions for a block synchronizing (indicating the starting position of the block), ID (identification) code, block address, parity check code, and audio data. At the mode I, audio data uses 2's complement codes of quantization bit of 16 bits of the sampling frequency of 48 kHz, and the PCM data is divided into 8 bits in higher order and 8 bits of lower order, modulated from 8 bits into 10 bits (8-10 modulation) and recorded in 10 bits.
In the sub-code region, information such as the number of musical piece recorded and time an elapsed during reproduction of the musical piece is recorded. A format of the sub-code region (for one block) is shown in FIG. 6.
For tracking control during reproducing in the R-DAT, an automatic tracking system with ATF is employed. ATF system detects and compares crosstalks from two adjacent tracks by ATF signals (see FIG. 4) recorded on the tracks, and controls the speed of the capstan motor for running tape so as to make crosstalks identical.
By this arrangement, the head A traces a track of azimuth + 20.degree. (hereinafter referred to as A track) whereas the head B traces a track of azimuth - 20.degree. (hereinafter referred to as B track). These heads A and B can trace width which is about 1.5 times as wide as the width of each track.
An R-DAT can be provided with a function of multiple speed or high speed reproduction corresponding to fast feeding reproduction (CUE F. F.) and rewinding reproduction (CUE REVIEW) provided in an analog type tape recorder. In the description to follow, multiple speed or high speed reproduction in the fast feeding direction will be referred to as "forward multiple speed reproduction" and multiple speed reproduction in the rewinding direction as "reverse multiple speed reproduction"). This multiple speed reproduction can be obtained by fast feeding or rewinding the tape while the mode is in reproduction mode.
During multiple speed reproduction, the head is released from the tracking control and crosses the tracks obliquely. In this case, recorded signals are reproduced in portions where the head A has crossed the A track and the head B has crossed the B track. Parts of a musical piece thereby are reproduced and multiple speed reproduction is realized.
An R-DAT has a function of reproducing and displaying, during a normal reproduction mode, the number of musical piece and time in a reproduced music piece which are recorded in the sub-code region of the tape. If sub-code information corresponding to a reproduced position is displayed in real time during also multiple speed reproduction, it will be very convenient for operations such as search (e.g., in case that reproduction should be started from a position at a specific time in a specific musical piece). Although each head passes over the sub-code region of either track in each tracing even during multiple speed reproduction, the head A does not necessarily trace the sub-code region of the A track and the head B that of the B track since the heads are not under the ATF control. When the head A traces the sub-code region of the B track and the head B traces the sub-code region of the A track, no sub-code is obtained with a result that the sub-code can only be reproduced intermittently.
The speed of multiple speed reproduction in the conventional R-DAT is integer multiple of a normal speed of reproduction. This however often causes a state in which the sub-code is not reproduced for a long period of time with resulting failure in real time display of sub-code information.
FIGS. 7 and 8 respectively show head traces on the tape in forward multiple speed reproduction and reverse multiple speed reproduction in the case of five-fold speed which is an odd number multiple speed in the integer multiple speed reproduction. A1, A2 etc. show trace of the head A and B1, B2 etc. show trace of the head B. The order of tracing is A1, B1, A2, B2 and so on. In multiple speed reproduction, the head trace does not become parallel with the tracks but crosses the tracks obliquely. In this case, amount of deviation between start position of the tracing and end position thereof changes as shown in FIG. 9 depending upon the times of speed in the multiple speed reproduction.
In FIGS. 7 and 8, the shaded portions represent portions of tracks in which the head A is tracing the A track and the head B is tracing the B track. Since the head trace is not parallel with the tracks, the width of these portions also undergo changes. The narrower the width of the shaded portion, the greater is the deviation between the head and the track and the lower is the output level, of the head. According to efficiency of the currently available head, recorded information can be read if this width is greater than about three quarters of the width of the track.
In multiple speed reproduction at integer multiple speed, interval produced between head traces becomes integer multiple of one track, whether it is an odd number or even number, so that positional relation between the head trace and the track becomes substantially the same pattern for the respective head traces.
In the five-fold speed trace state shown in FIGS. 7 and 8, patterns of sections in which recorded information can be read and those of sections in which recorded information cannot be read become as shown in (a) and (b) in FIG. 10 in which phase relation between the respective traces is the same. In this case, positional relation is such that the head A traces the A track in the sub-code position on the track and the head B traces the B track in the sub-code position so that the sub-code can be read trace by trace.
In multiple speed reproduction, however, the heads are released from the tracking control by ATF as described above and the positional relation as shown in FIGS. 7 and 8 have been obtained only accidentally. The positional relation between the head trace and the tracks is gradually deviated due to subtle variation in the rotation of the tape running capstan motor and stretching of the tape and becomes states as shown in FIGS. 11 and 12. In these states, patterns of sections in which recorded information can be read and those in which recorded information cannot be read become as shown in (c) and (d) in FIG. 10 in which phase relation between the traces becomes equal and the sub-code cannot be read in any section. These states continue until the positional relation between the head traces and the track is restored to the states shown in FIGS. 7 and 8 due to the above described element of instability. Since finally read sub-code information is held and displayed during a period of time when sub-code information cannot be read, sub-code information which precedes by far an actually reproduced position is displayed with resulting failure in real time display of sub-code information. Further, it is understood that a state that a substantial amount of PCM audio data also is dropped occurs.
If an even number multiple speed, e.g., four-fold speed or six-fold speed, among integer multiple speed is used, a range in which sub-code information can be read is broader than in the above described odd number multiple speed so that it has a better reading condition. The head trace pattern however is the same for the respective tracks so that deviation is caused in the manner of reading of sub-code information, e.g., the first sub-code (SUB CODE1 in FIG. 4) of the A track only is read and the first sub-code of the B track is not read at all. The inconvenience that sub-code cannot be read arises also in cases where a trouble has occurred in either one of the heads A and B or where there is a scratch ranging over a relatively long section in the longitudinal direction of the tape in which the sub-code to be read is recorded.
Thus, in the prior art integer multiple speed reproduction, sub-code information can either be read continuously or cannot be read at all continuously and, accordingly, this is very inconvenient for performing operations such as search. Besides, there is also a case where PCM data is not reproduced for a long period of time depending upon the positional relation between the head trace and the track.
It is an object of the invention to provide a magnetic recording and reproducing device which has eliminated the above described disadvantages of the prior art device and can successfully prevent a state in which information such as the number of music piece, position and time cannot be read continues from occurring over long period of time during multiple speed reproduction.